This present application relates generally to apparatus, methods and/or systems for improving the efficiency and/or operation of turbine engines. More specifically, but not by way of limitation, the present application relates to apparatus, methods and/or systems for cooling turbine airfoils via the circulation of a coolant through internal cooling circuits or passageways.
A gas turbine engine typically includes a compressor, a combustor, and a turbine. (Note that although the present invention may be described primarily in reference to an exemplary gas turbine engine, it is not so limited, and this reference is provided only as an example. A person of ordinary skill in the art will appreciate that embodiments of the present invention also may be used in aircraft engines and other types of rotary engines.) The compressor and turbine generally include rows of turbine blades or airfoils that are axially stacked in stages. Each stage may include alternating rows of circumferentially-spaced stator blades, which are fixed, and rows of circumferentially spaced rotor blades, that rotate about a central axis or shaft. In operation, the rotor blades in the compressor rotate about the shaft to compress a flow of air. The supply of compressed air then is used in the combustor to combust a supply of fuel. The resulting flow of hot gases from the combustion then is expanded through the turbine section of the engine, which induces the turbine rotor blades to rotate. With the rotor blades being connected to a central shaft, the rotation of the rotor blades induces the shaft to rotate.
In this manner, the energy contained in the fuel is converted into the mechanical energy of the rotating shaft, which may be used to rotate the rotor blades of the compressor, such that the supply of compressed air needed for combustion is produced, and the coils of a generator, such that electrical power is generated. During operation, because of the extreme temperatures of the hot-gas path, the velocity of the working fluid, and the rotational velocity of the engine, turbine airfoils, which, as described, generally include the rotating rotor blades and the fixed, circumferentially-spaced stator blades, become highly stressed with extreme mechanical and thermal loads.
Of course, the objective of designing and building more efficient turbine engines is a significant one, particularly considering the growing scarcity and increasing cost of fossil fuels. While several strategies for increasing the efficiency of turbine engines are known, it remains a challenging goal because the known alternatives, which, for example, include increasing the size of the engine, increasing the temperatures through the hot-gas path, and increasing the rotational velocities of the rotor blades, generally place additional strain on parts, including additional strain on turbine airfoils, which are already highly stressed. As a result, improved apparatus, methods and/or systems that reduce operational stresses placed on turbine airfoils or allow the turbine airfoils to better withstand these stresses are in great demand.
As one of ordinary skill in the art will appreciate, one strategy for alleviating thermal stresses is through cooling the airfoils such that the temperatures experienced by the airfoils are lower than that of the hot-gas path. Effective cooling may, for example, allow the airfoils to withstand higher firing temperatures, withstand greater mechanical stresses at high operating temperatures, and/or extend the part-life of the airfoil, all of which may allow the turbine engine to be more cost-effective and efficient. One way to cool airfoils during operation is through the use of internal cooling passageways or circuits. Generally, this involves passing a relatively cool supply of compressed air, which may be supplied by the compressor of the turbine engine, through internal cooling circuits within the airfoils. As the compressed air passes through the airfoil, it convectively cools the airfoil, which may allow the part to withstand firing temperatures that it otherwise could not.
In some instances, the supply of compressed air is released through small holes on the surface of the airfoils. Released in this manner, the supply of air forms a thin layer or film of relatively cool air at the surface of the airfoil, which both cools and insulates the part from the higher temperatures that surround it. This type of cooling, which is commonly referred to as “film cooling,” however, comes at an expense. The release of the compressed air in this manner over the surface of the airfoil, lowers the aero-efficiency of the engine, especially, in the case of nozzles or stator blades, if the air is released downstream of the throat. Better strategies that enhance the internal cooling through the airfoil such that film cooling could be minimized or reduced would generally increase the efficiency of the turbine engine. In addition, airfoils have cooling “dead spots,” which, generally, are locations that are difficult to cool because of certain fabrication and shape limitations of the airfoil. Finding ways to better cool these locations would benefit the useful life of the airfoils and increase the firing temperatures attainable by the engine. As a result, there is an ongoing need for improved cooling strategies for turbine airfoils.